This invention is especially useful in x-ray image intensifier systems which display an x-ray image on a television monitor and also record a corresponding image with cine or photospot cameras on film. However, the new video-photo frame size coordinator is useful in any system where a user wants to be sure that a region of interest for photorecording viewed on the television monitor will fall within the filme frame boundaries of the camera.
The invention will be illustrated in connection with an x-ray image intensifier system. In a system of this type an x-ray image intensifier tube is used to convert the x-ray image to an optical image which appears on an output phosphor of the tube. An objective lens is disposed with its axis coincident with the axis of the phosphor. A television camera is arranged for viewing the optical image. The television camera is coupled to a television monitor that displays the image on its screen. Because the input photocathode and output phosphor of image intensifier tubes are usually circular, the image or field of view which appears on the monitor screen is also circular.
X-ray image intensifier systems also provide for photographic recording of the image observed on the television screen. In some systems, one or the other or both a cine camera and a photospot camera is or are arranged to film and photograph the optical image on the phosphor while its counterpart appears on the television screen. Up to the time that the present invention was made, however, there has been no practical system or method for providing the cardiovascular radiologist or other operator of image recording system with an accurate indication of the portion of the image viewed on the television screen that will actually be recorded on the cine or photospot film.
Basically, the problem results from the fact that different cine and photospot cameras may use lenses of various focal lengths. When a camera happens to use a lens of a particular focal length, its frame size, of course, will be fixed. Similarly, for any given installation, the diameter of the circular image appearing on the television screen will also be fixed. However, the diameter of the image on the screen may be and, usually is, larger than the film frame size in which case segments of the circular image lying outside of the frame boundaries will be cut off and not recorded on the film. This may result in an object such as the heart, which is of interest in its entirety at the moment, falling in part within the boundaries of the film frame and in part outside of the boundaries in the segment which is visible on the television screen but which is cut off insofar as film recording is concerned. Thus, if the user can only see the circular image on the television screen there is presently no way of being sure that one or the other or both of the cameras is framing the entire area of interest.